. >> it is our responsibility and the responsibility of the president to use america's greatest power to shape history. >> reporter: both candidates have talked about relationships with china, but often in economic terms. neither has explained enough how he would deal with beijing diplomatically. china is now the world's second largest economy. it's also strengthens its military power and it's growing more assertive in territorial disputes. professor sew cha chin is an expert on foreign policy at american university in washington, d.c. he says both obama and romney would, if elected, continue the u.s. policy of engagement in the region. >> asia pacific is the natural choice for the policy of u.s. foreign policy given the very size of economy, and this is the most dynamic region in the world. think about u.s., china, japan. number one, number two, number three economies, all in asia pacific. zhao says the potential for conflict remains but the flash points have shifted. >> before there were two historically so-called hot spots may bring the two powers to war, one, korea peninsula, and